In the future we'll want to use this flag to signify if the release is an
upgrade, downgrade, below the version-lowest, or if it is locked in some way.
The libxmlb library is much faster to query, and does not require the daemon
to parse the XML metadata at startup. It's a zero-copy mmap design that is more
modern and less clunky.
RSS has reduced from 3Mb (peak 3.61Mb) to 1Mb (peak 1.07Mb) and the startup
time has gone from 280ms to 250ms.
